OK, solved, but now confused. The problem was that my /etc/apt/preferences files were different. When I changed the one on the core to what the one on my MD said, I got the versions to match- here's my core now:

Looks like the second one is the default preferences on a MD with the Mythtv added to it. All of my mds already had the preferences file and I just added the Mythtv part. my core is using the first one, and mds using the second one

I don't think those other rules affect us much, since the repositories we use only have Ubuntu 8.10 packages in them anyway. I believe it should be safe to remove them. I'm not sure why they would keep you from getting the newest version of MythTV .22 though... there must be something wrong with the MythTV package information.